The invention relates an apparatus and method for automatic discharging a thickened fraction from a centrifuge rotor. The arrangement according to this invention, is particularly suitable for but not limited to thickening of suspensions, where the specific mass of the thickened fraction thereof does not substantially differ from the specific mass of the starting suspension.
In the specification of U.S. Pat. No. 3,749,304 of the inventor herein, an automatic control arrangement for discharging a thickened fraction from a centrifuge rotor is described, based on the elastic deformation of elastically yielding bodies through which valve rods pass, opening and closing discharge valves on the circumference of the centrifuge rotor. These elastically yielding bodies are within a zone radial limit between an upper and lower level of the thickened fraction and as their deformation depends on the distribution of the hydrostatic pressure in their vicinity, these deformations can be utilized for the control of the position of valve rods with respect to discharge nozzles.
This prior art arrangement This arrangement operates as follows: so far as the level of the thickened fraction does not reach the elastically yielding body, the discharge nozzle remains closed by the valve rod. If however the level of the collected thickened fraction raises centripetally and starts to surround the elastically yielding body, the thickened fraction starts to act on this body due to its higher specific mass than the treated suspension by an increased pressure and to deform this body by pressure perpendicularly to the valve rod, lenghtening this body in direction towards the axis of the rotor. These deformations are transmitted by means of a strap plate to the valve rod, causing an opening of the discharge nozzle. If due to the opened discharge nozzle the level of the thickened fraction in the centrifuge rotor has dropped, the increased pressure on the elastically yielding body ceases, the body returns to its original state and the valve rod again closes the discharge nozzle. These described operations have a quick sequence, i.e. a relatively quick change of the closed to the opened position and vice versa takes place, as the movement of the valve rod is supported by the increase of the hydrostatic pressure acting on the face of the valve rod in the course of opening, and by a decrease of this pressure in the course of closing the nozzle.
The described arrangement operates satisfactorily for separating most suspensions, if, however, suspensions with a small difference of the specific mass of the thickened fraction with respect to the specific mass of the starting suspension have to be separated (for instance biological sludges, yeast dispersions and similar), the valve rods are actuated only if a substantial difference of the radial distance between the upper and lower level of the thickened suspension is reached. In the course of discharge of the thickened fraction and decrease of its level to the lower level, the thinner fraction are taken along, thus reducing the concentration of the resulting product.